This invention relates to a throttle stop controller for an automotive vehicle internal combustion engine and more particularly to the control of the throttle stop position to provide for smooth vehicle transmission upshifts when the throttle is released and to provide a smooth transition between power and coastdown operating modes of the vehicle.
It is well known in automotive engine controls to regulate the released (typically referred to as closed) position of the throttle in the throttle bore of the engine such as by controlling the position of a movable throttle stop in order to achieve a desired engine operating condition. The most common function of such regulation is the closed loop control of engine idle speed. When controlling the engine idle speed, the throttle position and therefore air intake quantity is actively regulated in response to measured engine speed to maintain a scheduled engine idle speed.
The need for a controlled transition to the idle speed control mode when the vehicle operator releases the throttle has long been recognized. For example, to prevent the engine speed from undershooting the idle speed, thereby giving rise to potential engine stalling, or to prevent the increase in hydrocarbon emissions resulting from a deficiency of air, it has been suggested that the released throttle position be established at some controlled transitional throttle angle.
One such known system for accomplishing this transitional control provides for extending the throttle stop corresponding to a predetermined small throttle angle such as 1.5 degrees each time the throttle is opened by the vehicle operator. When the throttle is released and engages the throttle stop, the throttle is held at the opened position established by the throttle stop for a predetermined constant time period after which the throttle angle during vehicle coastdown is controlled to a predetermined coastdown schedule. The coast don throttle angle control is continued until the vehicle speed becomes lower than an idle speed reference after which the idle speed control operating mode is enabled to control engine idle speed. The initial throttle angle represented by the throttle stop that is established when throttle is opened may typically be a function of coolant temperature, air conditioner clutch state and an altitude factor. The angle of the throttle established during the coastdown period while the vehicle speed is above the idle speed reference is typically a function of the engine temperature or vehicle speed.
An observation has been made in regard to the effect of the release of the throttle to the position established by the throttle stop including the position established by the known transitional controls set forth above. When the throttle is released by the vehicle operator while the vehicle transmission is experiencing an upshift or an upshift occurs in response to conditions resulting from the release of the throttle, the upshift may produce a sudden jerk of the vehicle resulting in poor vehicle ride quality. While this harsh let-up (released throttle) upshift may occur even when the automatic transmission converter clutch is deenergized during the shift, the upshift may be particularly severe in transmissions in which the converter clutch is energized to couple the input and output of the torque converter.
Even without a transmission upshift occurring on release of the throttle, let-up driveline lashing or bumping has been observed particularly if the transmission torque converter clutch is maintained energized or if the throttle was released from an engine accelerating condition to the coastdown throttle angle.
While the prior transitional throttle controls operate to prevent engine stalling and improve the emissions during the transition to the idle speed control mode of the engine, the controls are ineffective to alleviate the harsh upshift or driveline jerk that may result upon the release of the throttle.